US4161500A - Process for low attenuation methacrylate optical fiber - Google Patents

Process for low attenuation methacrylate optical fiber Download PDF

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Publication number
US4161500A
US4161500A US05/842,166 US84216677A US4161500A US 4161500 A US4161500 A US 4161500A US 84216677 A US84216677 A US 84216677A US 4161500 A US4161500 A US 4161500A
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Prior art keywords
polymer
temperature
core
methyl methacrylate
mol
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US05/842,166
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English (en)
Inventor
Henry M. Schleinitz
Paul G. Stephan
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Mitsubishi Rayon Co Ltd
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EI Du Pont de Nemours and Co
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Priority to US05/842,166 priority Critical patent/US4161500A/en
Priority to CA000313180A priority patent/CA1120197A/en
Priority to JP53124721A priority patent/JPS6018963B2/ja
Priority to DE19782844754 priority patent/DE2844754A1/de
Priority to GB7840407A priority patent/GB2006790B/en
Priority to DE2858225A priority patent/DE2858225C2/de
Priority to IT28756/78A priority patent/IT1099911B/it
Priority to FR7829289A priority patent/FR2405806A1/fr
Priority to DE2858163A priority patent/DE2858163C2/de
Priority to BE191100A priority patent/BE871239A/xx
Priority to NLAANVRAGE7810326,A priority patent/NL186527C/xx
Application granted granted Critical
Publication of US4161500A publication Critical patent/US4161500A/en
Assigned to MITSUBISHI RAYON COMPANY, LTD., A CORP OF JAPAN reassignment MITSUBISHI RAYON COMPANY, LTD., A CORP OF JAPAN ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: E.I. DU PONT DE NEMOURS AND COMPANY
Priority to JP57180056A priority patent/JPS6018964B2/ja
Priority to JP57180057A priority patent/JPS5878103A/ja
Priority to JP60126383A priority patent/JPS615206A/ja
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02033—Core or cladding made from organic material, e.g. polymeric material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D11/00—Producing optical elements, e.g. lenses or prisms
    • B29D11/00663—Production of light guides
    • B29D11/00721—Production of light guides involving preforms for the manufacture of light guides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/10—Esters
    • C08F220/12—Esters of monohydric alcohols or phenols
    • C08F220/16—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms
    • C08F220/18—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms with acrylic or methacrylic acids
    • C08F220/1802—C2-(meth)acrylate, e.g. ethyl (meth)acrylate
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/28—Formation of filaments, threads, or the like while mixing different spinning solutions or melts during the spinning operation; Spinnerette packs therefor
    • D01D5/30—Conjugate filaments; Spinnerette packs therefor
    • D01D5/34—Core-skin structure; Spinnerette packs therefor
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F8/00—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof
    • D01F8/04—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers
    • D01F8/10—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers with at least one other macromolecular compound obtained by reactions only involving carbon-to-carbon unsaturated bonds as constituent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/05—Filamentary, e.g. strands
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/10—Esters
    • C08F220/12—Esters of monohydric alcohols or phenols
    • C08F220/14—Methyl esters, e.g. methyl (meth)acrylate
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2913—Rod, strand, filament or fiber
    • Y10T428/2929—Bicomponent, conjugate, composite or collateral fibers or filaments [i.e., coextruded sheath-core or side-by-side type]

Definitions

  • the present invention relates to optical fiber which has a polymer core, and cladding of polymer which has an index of refraction lower than that of the core.
  • Optical fibers are well known in the art for transmission of light along a length of filament by multiple internal reflections of light. Great care is taken to minimize light losses due to absorption and scattering along the length of the filament, so that light applied to one end of the optical filamentary material is efficiently transmitted to the opposite end of the material.
  • the light transmitting portion or core of the optical filamentary material is surrounded by cladding having an index of refraction lower than that of the core, so as to achieve total internal reflection along the length of the filament.
  • This cladding is normally chosen to be transparent since an opaque cladding tends to absorb or scatter light.
  • optical fibers An important consideration in formation of optical fibers is minimization of any factor which increases the attenuation of transmitted light within such a fiber.
  • Optical fibers which consist wholly of inorganic glasses, or which have an inorganic glass core surrounded by a thermoplastic or thermosetting polymer, or which consist wholly of thermoplastic polymer, are all known in the art.
  • the all-plastic fibers are less subject to fracturing, but have the deficiency that they more strongly attenuate light passing therethrough.
  • the present invention is directed to improving the capability of all-plastic optical fibers to transmit light. It is also directed to a process for making high quality polymers of methyl methacrylate which are preeminently suitable for the core component of optical fibers.
  • an improved process for making an optical fiber which consists essentially of organic high polymers, said fiber consisting of a core and cladding, said core being fabricated of a first polymer which contains a major proportion of methyl methacrylate units, which comprises the steps
  • FIG. 1 is a schematic drawing, not to scale, of apparatus suitable for purifying methyl methacrylate and charging the polymerization vessel.
  • FIG. 2 is a drawing, partly schematic and partly cross-sectional, not to scale, of apparatus suitable for making optical fiber from a polymer preform.
  • Pursuant to making an all-plastic optical fiber capable of high transmission of light therethrough it is important to use monomer of high quality. To this end, it is important to remove from the monomers, especially those from which the core of the fiber will be made, those substances which if retained would absorb or scatter light introduced into the optical fiber made therefrom.
  • the core of the fiber is a copolymer containing at least 60 mol %, preferably at least 80 mol %, most preferably at least 90 mol % of methyl methacrylate, or polymethyl methacrylate polymer itself.
  • monomers such as acrylic esters, e.g., methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate; methacrylic esters, e.g., cyclohexyl methacrylate, benzyl methacrylate, ethyl methacrylate, propyl methacrylate and butyl methacrylate; or styrene may be used.
  • At least 90 mol % of the core polymer be composed of methyl methacrylate, so as to have high light transmission.
  • the most highly preferred copolymers are those prepared from at least 95 mol % of methyl methacrylate and 0 to 5 mol % of methyl acrylate, ethyl acrylate or ethyl methacrylate.
  • the copolymers are preferred because they have greater flexibility, and are less subject to thermal depolymerization, compared to homopolymer of methyl methacrylate.
  • Partially or completely deuterated vinyl monomers can also be used to make polymers for optical fibers.
  • the resulting fibers like their non-deuterated counterparts, are optically transparent, the wavelengths at which minimum attenuation of transmitted light occurs being shifted.
  • a particularly useful deuterated monomer is methyl methacrylate-d 8 . Lowest attenuation of light at the wavelengths of maximum transmission is attained as the amount of C--H bonds (as distinct from C--D bonds) in the core polymer is minimized.
  • methyl methacrylate ordinarily contains biacetyl, and that the amount of biacetyl should be reduced to no more than about 10 ppm (parts per million), preferably no more than 5 ppm. Removal of the impurities can be accomplished by treatment with alumina, followed by distillation.
  • alumina Although any type of alumina can be used, for most effective removal of impurities it is best to use basic alumina and that it be of activity grade 1. Such treatment removes or reduces the amount of compounds having labile hydrogen and of highly polar compounds such as biacetyl.
  • the treatment can be accomplished prior to distillation of the monomer by placing the alumina on a filter which will retain it, and filtering the monomer through the alumina directly into the still pot. This operation is suitably carried out under a nitrogen atmosphere.
  • Transition metal ions especially those of transition elements of the first series (i.e., elements of atomic number 22 through 28), and copper, lead, aluminum, silicon, vanadium, chromium, manganese, iron and nickel are also deleterious impurities, because they absorb light of wavelengths which the optical fiber is intended to carry.
  • the amount of such impurities can also be conveniently lowered to acceptable levels by distillation.
  • the amount of such impurities should be no greater than about 500 ppb (parts per billion), preferably no greater than 100 ppb, total for all such ions present.
  • Particulate matter should also be removed because these particles absorb and/or scatter light.
  • the monomers (and the other components of the polymerization charge) should be substantially free of such particulate matter.
  • particles smaller than about 200 nm (0.2 ⁇ m) cannot be resolved with an optical microscope, with the use of a transverse intense beam of light in an optical microscope points of light are observed in an optical fiber not only at the particles which are larger than about 200 nm, but also at smaller particles of undetermined size. Even though it is not possible to precisely determine the sizes of these particles, it is nevertheless important to remove those, regardless of size, which are detectable by light scattered from the particle.
  • Particles of all sizes can be effectively removed by distillation of the monomers, providing that the distillation is carried out such that there is no entrainment.
  • the best (i.e., cleanest) commercially available polymers have on the order of 300 to 1000 particles/mm 3 , and can provide optical fibers with attenuations of light down to ca. 500 dB/km and having at best a few short lengths as low as 400 dB/km.
  • optical fibers having no more than 100 particles/mm 3 are easily made.
  • Particle counts below 10 particles/mm 3 are also easily attained by the present invention, and counts below 2 particles/mm 3 have been attained. Accordingly, in reference to the monomers, by “substantially free” is meant that the mixed vinyl monomers contain no more than about 100 particles/mm 3 .
  • Any comonomer used should be similarly purified, but such purification ordinarily need not be as rigorous, especially when the amount used is less than 10 mol % of the total monomer because less impurity is introduced with the smaller quantity of monomer and is diluted upon mixing the monomers.
  • distillation When distillation is employed as the method of purification, the distillation is conducted under a slight positive pressure of an inert gas such as argon, nitrogen or helium. As is known in the art, so as to prevent polymerization of monomer in the fractionating column, a concentrated solution of polymerization inhibitor in the same monomer is introduced at the top of the column throughout the fractionation.
  • an inert gas such as argon, nitrogen or helium.
  • Polymerization is carried out with the use of a soluble free radical polymerization initiator, ordinarily an azo type initiator.
  • a soluble free radical polymerization initiator ordinarily an azo type initiator.
  • the initiator type and concentration are chosen to provide about 50% conversion to polymer in about 16 hrs.
  • an initiator having a half-life at 60° C. between about 300 and 3,000 minutes, preferably about 1,000 minutes.
  • 2,2'-azo-bis(isobutyronitrile) is the preferred initiator because it is available in high purity and because it can be handled safely.
  • initiators with somewhat longer or shorter half-lives such as 1,1'-azo-bis(cyclohexanecarbonitrile) or 2,2'-azo-bis(2,4-dimethylvaleronitrile
  • 1,1'-azo-bis(cyclohexanecarbonitrile) or 2,2'-azo-bis(2,4-dimethylvaleronitrile) can also be used; for those having longer half-lives, the temperatures of the heating stages used during polymerization, especially the first stage, will have to be higher than when 2,2'-azo-bis(isobutyronitrile) is used, and/or greater amounts can be used, and conversely, for those having shorter half-lives, the temperatures of the heating stages used during polymerization, especially the first stage, will have to be lower, and/or smaller amounts may be used.
  • initiator any combination of initiator, initiator concentration and polymerization temperature can be used. Combinations of initiators having different half-lives can also be used. The initiator and its concentration are so chosen that some will remain for the later heating stages of the polymerization step. A high purity initiator should be used so as to introduce the least possible amount of impurity into the resulting polymer.
  • a chain transfer agent is also included in the polymerization system. Both mono- and multifunctional chain transfer agents can be used. Typical examples include n-butyl mercaptan, lauryl mercaptan, mercaptoacetic acid, 2,2'-dimercaptodiethyl ether, ethylene bis(2-mercaptoacetate) commonly referred to as glycol dimercaptoacetate (GDMA), ethylene bis(3-mercaptopropionate), 1,1,1,-trimethylolethane tris(3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate).
  • GDMA glycol dimercaptoacetate
  • GDMA ethylene bis(3-mercaptopropionate
  • 1,1,1,-trimethylolethane tris(3-mercaptopropionate) pentaerythritol tetrakis (3-mercaptopropionate).
  • the preferred chain transfer agents are those having mercaptan groups on carbon atoms adjacent to the carbonyl of a carboxylic functional group, i.e., of the type disclosed in U.S. Pat. No. 3,154,600, and having mercaptan difunctionality, because their use generally provides polymer of higher conversion and optical fiber having higher light transmission when compared to those prepared with other chain transfer agents. It is preferred to purify the chain transfer agent, which can be done by distillation.
  • the quantities of initiator and chain transfer agent are so chosen to give a polymer having an inherent viscosity of at least about 0.4 dl/g, as measured at 25° C. on a 0.5% (wt./vol.) solution in chloroform (i.e., 0.5 g of polymer in 100 ml. of solution). At inherent viscosities of 0.38 dl/g or lower the polymer is more brittle, while at 0.4 dl/g and higher the polymer is reliably tough. Although polymers having inherent viscosities as high as 0.5 and 0.6 can be used, they are difficult to extrude because they are so viscous at temperatures which are suitable for extrusion without polymer degradation that special heavy duty equipment is required.
  • Polymers having an inherent viscosity in the range 0.40 to 0.44 are tough and do not require heavy-duty equipment, and thus are preferred. Further, it is difficult to extrude the very high viscosity polymer into fibers having a smooth, fracture-free surface, as most often the extrudate will have a fractured surface which directly causes a much higher attenuation of transmitted light. To achieve an inherent viscosity in the preferred range, appropriate amounts of the polymerization initiator and chain transfer agent are easily determined empirically.
  • the polymerization initiator is ordinarily used in an amount of about 0.001 to 0.05 mol %, based on the total monomer and for the preferred initiator preferably 0.01 to 0.02 mol %, and the chain transfer agent is ordinarily used in an amount of about 0.1 to 0.5 mol %, based on the total monomer, and for the preferred difunctional chain transfer agents preferably in the range of 0.1 to 0.25 mol %.
  • a convenient sequential arrangement begins with a still pot 1 equipped with a column 2 packed, for example, with glass helices, and having a volumetrically calibrated receiving vessel 3 which is connected to a mixing vessel 4 by a line which is equipped with a greaseless stopcock or other type of greaseless valve 5.
  • the mixing vessel 4 is equipped with a magnetically driven stirrer 6 and an entrance port 7 which is sealed by a serum stopper 8 and a stopcock 9, and is connected to a microporous filter 10 by a line which is equipped with a greaseless stopcock 11 or other type of greaseless valve.
  • distilled monomer is introduced into the mixing vessel 4 through the entrance port 7, other arrangements are also possible wherein the monomer is transferred from receiver 3 to vessel 4 through a line separate from the entrance port 7.
  • the filter 10 is of known type which is inert to all constitutents of the polymerization mixture, such as polytetrafluoroethylene, supported on a porous metal plate.
  • the pore size of the filter can range from 1 micrometer down to about one-twentieth of the wavelength of light to be carried by the optical fiber, and is preferably in the range of 0.2 to 1 micrometer.
  • the filter 10 is in turn connected by a line 29 to the polymerization vessel 12.
  • An inert atmosphere such as argon, helium or nitrogen, is maintained throughout the whole arrangement of apparatus by introduction through gas inlets 13 and 14, and its flow is controlled and directed by the various stopcocks 15, 16, 17 and others shown.
  • the various elements of the apparatus can be broken down into smaller units by ground glass joints, ring seals, or other known means not shown.
  • methyl methacrylate is introduced into still pot 1 through a filtering vessel 18 which contains a filter element 19 which supports a bed of alumina 20. Following charging of the pot, stopcock 21 is closed.
  • the packed column 2, still head 22, condenser 23 and needle valve 24 function in known manner to control take-off of distillate.
  • Polymerization inhibitor is introduced from a liquid reservoir 25 and its flow is controlled by stopcock 26.
  • a foreshot to be discarded is removed through outlet 27 controlled by stopcock 28.
  • the desired center distillate fraction is collected in the receiving vessel 3.
  • a first portion of distilled methyl methacrylate is transferred through the connecting line from the distillation receiver to the mixing vessel 4.
  • a solution of the desired polymerization initiator and chain transfer agent in the desired amounts in the comonomer, or, if no comonomer is used, in a small, measured amount of separately purified methyl methacrylate is introduced into the mixing vessel through the entry port 7 with the aid of a hypodermic syringe inserted through the serum stopper 8 and stopcock 9.
  • a second portion of distilled methyl methacrylate is transferred through the connecting line from the distillation receiver 3 to the mixing vessel 4.
  • the purpose of reserving part of the methyl methacrylate for the final addition to the mixing vessel is for washing all traces of the minor components of the polymerization mixture, i.e., the comonomer, polymerization initiator and chain transfer agent, from the entry port 7 into the mixing vessel 4; loss of part of the minor components by adhering within the entry port would lead to a greater degree of nonuniformity of the resulting polymer among successively run polymerizations, as compared to the loss of a trace of the major constituent, methyl methacrylate, within the entry port.
  • the combined materials are thoroughly mixed with the magnetic stirrer 6 to assure homogeneity.
  • the mixture is then passed through the filter 10, and into the polymerization vessel 12.
  • the polymer is prepared in the shape of a preform suitable for the barrel of the ram extruder to be used in making the core of the optical fiber.
  • the polymerization vessel 12 is thus of a shape to make the required polymer preform. Because of the manner in which a ram extruder operates, the preform will ordinarily be in the shape of a rod. Although rods of various cross-sectional shapes could be used, a circular cross-section is most suitable, because the most convenient cross-sectional shape for fabrication of the polymerization vessel and extruder barrel is circular. Additionally, polymer rods which are cylindrical are preferred because such rods lead to maximum uniformity during extrusion, and thus an optical fiber core having more uniform properties.
  • the polymerization vessel 12 is fabricated of metal of sufficient thickness to withstand the pressure level to be employed during polymerization, typically a pressure in the range of 7 to 25 kg/cm 2 .
  • Suitable materials of construction include the stainless steels. So as to preclude contamination of the polymer by transition metal ions at even the parts-per-billion level, it is preferred to plate the cavity of the polymerization vessel with an inert metal such as gold or chromium.
  • the polymerization vessel 12 is sealed at its lower end with a piston 30 having a gasket.
  • the polymerization vessel is removed from the sealed or closed system described above by removal of plug 31 and immediately sealed with a piston (not shown) which is like piston 30 and which fits its cylindrical cavity. Sealing with the piston is done without delay so as to avoid contamination by dust or any foreign substance by exposure to the atmosphere.
  • the gasket of each piston is fabricated of a material which is inert to all components of the polymerization mixture at the temperatures employed, such as polytetrafluoroethylene, to prevent contamination of the polymerization mixture and resulting polymer.
  • the polymerization should be carried out without any free gas space being present in the polymerization vessel.
  • the presence of gas in such space results in gas being present in the polymer preform, both dissolved therein and in the form of bubbles, which leads to an extruded core which contains bubbles or voids and thereby attenuates transmitted light more than a core without bubbles or voids.
  • various methods can be used to exclude all free gas space from the vessel.
  • One suitable method is to fabricate the polymerization vessel 12 with a bleed hole 32 of small diameter (typically less than 1 mm) located a short distance from the open end of the vessel.
  • the vessel is filled with polymerization mixture to above the bleed hole, and the piston seal is put into place and pushed into the cavity until all free gas and excess liquid mixture is forced from the bleed hole and the piston seals off the liquid in the major part of the cavity so that it is isolated from the bleed hole.
  • the polymerization is carried out under pressure, suitably 7 to 25 kg/cm 2 (100 to 350 psig), to preclude vaporization of monomer and consequent formation of bubbles or voids in the polymer preform, for reasons similar to those set forth in the previous paragraph. Pressure is maintained by applying force against the piston seals throughout the reaction with a press.
  • Maintaining the polymerization mixture under pressure also provides a means of assessing the progress of polymerization, which information is used during the course of polymerization in setting the heating program employed.
  • Maintaining the polymerization mixture under pressure it is possible to follow the progress of the polymerization dilatometrically, i.e., by following the change in volume of the mixture.
  • the mixture assumes a smaller volume upon polymerizing, the polymer occupying a volume of the order of about 80% of that of the monomers.
  • Progress of the polymerization can be followed, for example, by placing an index mark on the rod used to transmit force to one of the piston seals at such a position that it will remain visible outside the cavity of the polymerization vessel throughout the polymerization, and following its change in position with a cathetometer. From the initial volume of the reactants employed, the final volume of polymer to be prepared as determined if necessary from preliminary runs, and the initial position of the index mark, it is a simple matter to estimate where the index mark will be when polymerization has progressed to any given percentage of completion.
  • the polymerization mixture is carefully and progressively heated to higher temperatures in such manner as to attain at least 98% conversion to polymer, but to prevent development of an uncontrolled or "runaway" reaction, which would lead to a thermally degraded product.
  • the mixture is first maintained below about 70° C., preferably between 60° C. and 70° C., until conversion to polymer is at least 60% complete, preferably 65 to 75% complete.
  • the mixture is next heated to raise the temperature at a rate to reach 90° to 100° C. at the time that conversion to polymer is at least 95% complete.
  • Heating to raise the temperature at about the same rate is continued until a temperature in the range of 115° to 140° C., preferably 125°-135° C., is attained, and finally a temperature in the same range is maintained for at least one half hour, preferably at least one hour.
  • the resulting polymer is then cooled. Pressure in the range of 7 to 25 kg/cm 2 is maintained during the entire heating program. The pressure is released only after the temperature of the polymer has dropped below 100° C., which is the boiling point of methyl methacrylate, so as to preclude formation of bubbles by traces of residual monomer.
  • the specific rate of heating will vary to some extent, but the conditions will always conform to the schedule of the previous paragraph.
  • the diameter is 28.7 mm (1.13 in)
  • the mixture is heated to raise the temperature at a rate of 35° to 45° C. per hour until a temperature of 115° to 140° C. is attained, which rate will result in at least 95% conversion to polymer when a temperature of 90° to 100° C. is attained.
  • a rate of temperature increase which is the same or faster can be used.
  • a slower rate of temperature increase is required.
  • the polymer preform is then transferred from the polymerization vessel 12 to the barrel 52 of a ram extruder 51 shown in FIG. 2.
  • the preform is fabricated in a shape which closely matches the barrel 52 of the ram extruder.
  • the inside diameter of the extruder barrel is suitably slightly greater than the inside diameter of the polymerization vessel.
  • the preform should not be handled, or retained exposed to the atmosphere unduly, so as to minimize contamination of the preform with dust, oils from the skin, etc. It is best to transfer the preform without touching it, but if handling is necessary, lint-free gloves should be worn.
  • the preform is then extruded by advancing the preform through the barrel 52 with a ram 53 toward an extrusion orifice 54 through which the polymer is forced to form the core of the fiber.
  • the ram can be either of the constant rate type, or the constant stress type, the latter being used in combination with a melt metering pump such as a gear pump.
  • the constant rate ram is preferred because its use does not require a melt metering pump, the use of which pump introduces a potential opportunity to contaminate the polymer with foreign particles.
  • the extrusion barrel 52 is heated only at its forward end by heating elements 55, 55' so that the polymer is softened just before it is forced through the extrusion orifice 54.
  • cooling coils 56, 56' are preferably installed to prevent conduction of heat along the barrel 52 and consequent heating of polymer farther away from the orifice. Operation in this manner results in reheating of the polymer for the minimal time needed to extrude it into fiber form, and consequently minimizes opportunity for thermal degradation of the polymer to substances which will impair the optical transparency of the fiber.
  • the temperatures employed for extrusion will vary somewhat with the polymer composition, but for the polymethyl methacrylate polymers described hereinabove, the temperature of the spinning head 57 will ordinarily be in the range of about 200°-240° C. and about 220°-280° C. at the forward end of the barrel where the preform is softened.
  • the preferred temperatures are 210°-220° C. at the spinning head and 240°-250° C. at the forward end of the barrel.
  • the cladding of the optical fiber can be applied to the core by various methods. Such methods include coextrusion and solution coating, both of which methods are well known in the art. By coextrusion is meant an operation wherein both core and cladding polymers are fed through the same orifice 59 in spinneret plate 58 from which is extruded a composite fiber 60 wherein the core polymer is completely surrounded by a substantially uniform thin layer of the cladding polymer. Coextrusion is the preferred method for making optical fibers in the present invention. Solution coating, however, is also a practical method, and, if employed, should be carried out as an in-line process step just after extrusion of the core, so as to minimize opportunity for the core to be contaminated by any material, such as particles of dust or dirt.
  • the spinning head 57 is of known type such as described in U.S. Pat. No. 3,992,499, specifically of the type shown in the left-hand part of FIG. 1 thereof.
  • the spinning head 57 has a spinneret plate 58 and a meter plate 65 in a body 66.
  • the core polymer is led from the orifice 54 of ram extruder 51 to the spinning head 57 by line 61, and is shown as molten core polymer stream 68.
  • the cladding polymer is introduced from reservoir 62 into conventional screw extruder 63 and metered by melt metering pump 64 into the spinning head 57, and is shown as molten cladding polymer stream 69.
  • the cladding polymer applied to the core is optically transparent and has an index of refraction at least 0.1% lower than that of the core, preferably at least 1% lower, and most preferably at least 5% lower.
  • suitable cladding materials include those disclosed in British Patent Specification No. 1,037,498 such as polymers and interpolymers of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoromethyltrifluorovinyl ether, perfluoropropyltrifluorovinyl ether and fluorinated esters of acrylic or methacrylic acids having the structure ##STR1## wherein X is selected from the group consisting of F, H, or Cl, and n is an integer of from 2 to 10, m is an integer from 1 to 6 and Y is either CH 3 or H, and copolymers thereof with esters of acrylic and methacrylic acids with lower alcohols such as methanol and ethanol. Copolymers of ##STR2## where X, Y, m and n are as defined above with the methyl and ethyl esters of acrylic and methacrylic acids and which are substantially amorphous constitute
  • Fluorinated polymers which contain pendant side chains containing sulfonyl groups such as disclosed in U.S. Pat. No. 3,849,243, and fluorine-containing elastomers such as those disclosed in U.S. Pat. Nos. 2,968,649 and 3,051,677 can also be used.
  • Others include copolymers of tetrafluoroethylene with other monomers such as hexafluoropropylene and perfluoroalkyl perfluorovinyl ether as disclosed in U.S. Pat. Nos. 2,946,763 and 3,132,123. Modified and unmodified copolymers of tetrafluoroethylene and ethylene as disclosed in U.S. Pat. No. 2,468,664 can also be used.
  • Cladding polymers which are not crystalline, i.e., which are substantially amorphous, are preferred, because optical fibers clad with a crystalline polymer tend to have higher attenuations of transmitted light than those coated with an amorphous polymer.
  • Optical fibers clad with a crystalline polymer do have utility, particularly when only a short length of optical fiber or cable is needed.
  • the core and cladding should be polymers which will not soften at the high temperatures, and many polymers suitable in such cases tend to be crystalline.
  • the diameter of the extrusion orifice 59 can vary, depending on the desired fiber diameter, and the amount of melt draw down taken.
  • the fiber is drawn immediately after it exits from the spinning head and while it is still in a heat-softened state in order to induce molecular orientation for the purpose of imparting toughness to the fiber.
  • the machine draw ratio is the ratio of the cross-sectional area of the die orifice to the cross-sectional area of the optical fiber if it is made by coextrusion or to the cross-sectional area of the core of the optical fiber if it is made by solution coating.
  • the diameter of the core of the optical fiber can vary from relatively thin to relatively thick constructions.
  • a suitable diameter range is 50 to 500 ⁇ m.
  • the light source is large, e.g., from an LED (light emitting diode)
  • a thick core has the advantage in its ability to capture a greater proportion of incident light, but has the disadvantage of having a larger minimum bending radius.
  • the light source is small, e.g., a laser, a relatively thin core is suitable for capturing incident light and has the advantage of a smaller minimum bending radius.
  • the thickness of the cladding generally is not critical, so long as its thickness is at least a few wavelengths of the light to be transmitted.
  • An example of a suitable range of thickness of the cladding is about 5 to 50 ⁇ m, preferably 10 to 20 ⁇ m.
  • Line speed following extrusion can vary widely, depending on the capability of the equipment employed. Line speeds of 15 to 90 m/min (50 to 300 ft/min) are typical, but higher and lower speeds can also be used. Speeds in the range of 35 to 60 m/min (120 to 200 ft/min) provide highly satisfactory results.
  • a cross-flow of air blown by means not shown can be used to quench the freshly extruded fiber; air flow velocities of 3 to 15 cm/sec (0.1 to 0.5 ft/sec) are suitable.
  • the drawn optical fiber is wound up on drum 67.
  • Optical fibers made in accordance with the present invention have remarkably low attenuations of transmitted light.
  • Optical fibers having attenuations of less than 400 dB/km (decibles per kilometer) at 656 nm are routinely made by the present invention, and attenuations below 300 dB/km, such as 274 dB/km, have been attained.
  • Attenuation of transmitted light was measured as described by E. A. J. Marcatili, "Factors Affecting Practical Attenuation and Dispersion Measurements," Optical Fiber Transmission II, Technical Digest, Optical Society of America, 1977, paper TuEl.
  • the light source was a tungsten-halogen (incandescent) projector lamp powered by a DC voltage and current stabilized supply, and the wavelength used was selected with an interference filter having a peak wavelength of 656.3 nm, band width of 10 nm, 50% minimum transmission and average transmission of side bands of 10 -4 , specifically, an Ealing-IRI interference filter 26-9357 (76-77 catalog).
  • the input end of the fiber was placed at the circle of least confusion of the source. Numerous experiments indicated that the log 10 power was linear with length, and therefore that for practical purposes transmission was at a steady state.
  • a 200-ml round-bottom flask was charged with 100 ml of glycol dimercapto acetate (Evans Chemetics, Inc., indicated to be 96.6% pure). Distillation was conducted with a 20-cm Vigreau column. A 20-ml foreshot was collected at 0.28 to 0.2 mm Hg absolute at condensing temperature of 80° to 118° C. and discarded. A 60-ml cut for use in polymerization runs was collected at 0.18-0.12 mm Hg absolute at condensing temperatures of 115°-122° C. Analysis by gas-liquid chromatography indicated 99% purity.
  • a 1650-ml charge of methyl methacrylate monomer (Du Pont Type H112, which contains hydroquinone inhibitor) was permitted to flow by gravity through a 90-mm diameter ⁇ 8-cm deep bed of basic aluminum oxide into a 2-l round-bottom flask containing 0.5 g DPPD inhibitor.
  • the monomer was distilled through a 25-mm diameter ⁇ 56-cm high column packed with glass helices at a high reflux ratio. Four hundred ml were collected as a foreshot at condensing temperatures up to 101° C. at atmospheric pressure and discarded; the still was cooled and blanketed with filtered argon.
  • the MMA was mixed in receiving vessel 3 of FIG. 1 with a magnetically driven magnet (not shown in FIG. 1) coated with polytetrafluoroethylene (PTFE).
  • PTFE polytetrafluoroethylene
  • Half of the mixture was discharged by argon pressure through an 0.2 ⁇ m (micrometer) pore "Millipore” filter and an FEP (copolymer of tetrafluoroethylene and hexafluoropropylene) tube into a rigorously cleaned chromium-plated stainless steel tube having an inside diameter of 28.7 mm (1.13 in) sealed at the bottom with a PTFE "O" ring gasketed stainless steel piston and at the top with a PTFE plug. After filling the tube, the PTFE plug was removed and immediately replaced with a PTFE gasketed piston. The second half of the monomer mixture was similarly discharged into a gold-plated stainless steel tube sealed with gold plated pistons. The sealed gold plated tube was placed in a freezer at -20° C.
  • the chromium-plated tube was placed in a heat transfer jacket and the contents were pressurized to 24.3 kg/cm 2 (345 psig) by a pneumatic cylinder operating on the top piston. Silicone heat transfer fluid was pumped through the jacket according to the following schedule:
  • the polymer rod was removed from the polymerization tube, small samples were taken for analysis, and the rod was placed in a polyethylene bag without handling and overwrapped with aluminum foil.
  • the contents of the gold-plated tube were polymerized in the same fashion. Properties of the polymers are given in Table I.
  • the extrusion equipment as described herein in FIG. 2 was employed, with a spinning temperature of 215° C. and a line speed of 36.6 m/min (120 ft/min).
  • the core of the optical fiber was made from the polymer rod fabricated in part D of this example, which was extruded by the constant rate ram extrusion method.
  • the cladding polymer which was extruded with a conventional screw extruder, was a copolymer of 20% by weight of methyl methacrylate and 80% by weight of ##STR3## (p is 1 to 8, with ca.
  • the perform made in the gold-plated tube was similarly used to make optical fiber.
  • Example 1 was repeated in a chromium-plated polymerization tube, but with the following differences.
  • the concentration of EA comonomer was 0.5 mol %.
  • Example 2B 60° C. was maintained for 15.75 hrs. and in Example 2A, the final temperature employed was 120° C.
  • spinning temperature was 225° C.
  • Example 2B 220° C.
  • Example 1 was repeated in a chromium-plated polymerization vessel, but with the following differences, a variable amount of EA comonomer was used in three runs as indicated in Table III. During spinning of fibers, the spinning temperature was 214° C. in Examples 3A and 3C, and 215° C. in Example 3B. Property data are shown in Table III.
  • Example 1 was repeated in a chromium-plated polymerization vessel, but with the following differences.
  • the ethyl acrylate comonomer concentration was varied as shown in Table IV.
  • Various chain transfer agents were used, as indicated in the table.
  • the spinning temperature was 215° C. in Examples 4A and 4C, and 214° C. in Example 4B.
  • Example 1 was repeated in a chromium-plated pressure vessel, but with the following differences.
  • the amount of EA comonomer and the type and amount of chain transfer agent were varied, and the sealing gaskets on the piston closures of the polymerization tube were varied. Most importantly, the final temperature was varied to demonstrate the effect of that variable. Those variables and properties are summarized in Table V.
  • Example 1 was repeated in a chromium-plated polymerization vessel, but with the following differences.
  • the chain transfer agent and piston seals were varied.
  • the spinning temperature was raised to 225° C. in Example 6B, which caused the fiber to exhibit a somewhat higher number of breaks; this lower toughness is associated with a lower degree of axial molecular chain orientation.
  • Table VI The data are summarized in Table VI.
  • Example 1 was repeated twice in a chromium-plated polymerization vessel, but with the following differences. No comonomer was used, i.e., the monomer was all methyl methacrylate. In both cases, the residual monomer was in the range 0.7 to 1.05% by wt. Spinning temperatures were 214° C. in Example 7 and 216° C. in Control B.
  • Example 7 the optical fiber had an attenuation at 656 nm of 316 dB/km (0.73 cm -1 ⁇ 10 3 ).
  • Control B the polymer preform was handled by several people, then cleaned as thoroughly as possible before extrusion; the optical fiber had attenuations in the range 753 to 884 dB/km (1.7 to 1.9 cm -1 ⁇ 10 3 ). This demonstrates the care which must be exercized to avoid deleterious contamination of the polymer.
  • Example 1 was repeated twice in a chromium-plated polymerization vessel.
  • the optical fiber produced had an attenuation of 319 dB/km at 656 nm.
  • Example 1 was repeated in a chromium-plated polymerization vessel, but using deuterated methyl methacrylate in place of the MMA, and only one preform was prepared.
  • the monomer used was 99.88% MMA-d 8 and 0.113% of approximately equal amounts of methyl-d 3 acrylate and methyl-d 3 acrylate-2,2-d 2 .
  • Into 260 ml of the monomer was placed 1.37 ml of a solution of 0.0803 g of Vazo® 64 and 1.24 ml of GDMA in another 1.50 ml of the MMA-d 8 . This gave a GDMA concentration 0.16 mol %, based on monomer.
  • the heating schedule was as follows.
  • the deuterated polymer obtained had an inherent viscosity of 0.426 dl/g, and contained 1.17 wt % residual monomer.
  • the polymer contained 239 ⁇ g of proton per gram of polymer, as determined by nuclear magnetic resonance at 60 MHz. Maximum transmission of light occurred at wavelengths of 690 and 790 nm, at which wavelengths the attenuation of light was 225 dB/km.

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US05/842,166 1977-10-14 1977-10-14 Process for low attenuation methacrylate optical fiber Expired - Lifetime US4161500A (en)

Priority Applications (14)

Application Number Priority Date Filing Date Title
US05/842,166 US4161500A (en) 1977-10-14 1977-10-14 Process for low attenuation methacrylate optical fiber
JP53124721A JPS6018963B2 (ja) 1977-10-14 1978-10-12 低減衰全プラスチックオプチカル・ファイバ−の製造方法
CA000313180A CA1120197A (en) 1977-10-14 1978-10-12 Low attenuation all plastic optical fiber
NLAANVRAGE7810326,A NL186527C (nl) 1977-10-14 1978-10-13 Werkwijze voor de vervaardiging van een optische vezel.
DE2858225A DE2858225C2 (ja) 1977-10-14 1978-10-13
IT28756/78A IT1099911B (it) 1977-10-14 1978-10-13 Fibra ottica a bassa attenuazione fatta totalmente di materiale plastico
FR7829289A FR2405806A1 (fr) 1977-10-14 1978-10-13 Procede de fabrication d'une fibre optique en matieres polymeres
DE2858163A DE2858163C2 (ja) 1977-10-14 1978-10-13
DE19782844754 DE2844754A1 (de) 1977-10-14 1978-10-13 Optische faser mit geringer abschwaechung
GB7840407A GB2006790B (en) 1977-10-14 1978-10-13 Low attenuation all-plastic optical fibre
BE191100A BE871239A (fr) 1977-10-14 1978-10-13 Procede de fabrication d'une fibre optique en matieres polymeres
JP57180056A JPS6018964B2 (ja) 1977-10-14 1982-10-15 メチルメタクリレ−ト系重合体の製造法
JP57180057A JPS5878103A (ja) 1977-10-14 1982-10-15 低減衰全プラスチツクオプテイカル・フアイバ−の製造法
JP60126383A JPS615206A (ja) 1977-10-14 1985-06-12 オプテイカル・フアイバーの予備成形体の製造方法

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JPS5784403A (en) * 1980-11-14 1982-05-26 Nippon Telegr & Teleph Corp <Ntt> Method and device for production of low loss plastic optical fiber
JPS5781205A (en) * 1980-11-11 1982-05-21 Nippon Telegr & Teleph Corp <Ntt> Low-loss plastic optical fiber and its production
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JPS58118603A (ja) * 1982-01-07 1983-07-14 Mitsubishi Rayon Co Ltd 光学繊維の製造法
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JP2555576B2 (ja) * 1987-01-06 1996-11-20 東レ株式会社 耐熱分解性に優れたプラスチック光ファイバ
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US4353960A (en) * 1978-09-21 1982-10-12 Kureha Kagaku Kogyo Kabushiki Kaisha Composite and conjugate filaments
US4278634A (en) * 1980-08-18 1981-07-14 American Cyanamid Company Biconstituent acrylic fibers by melt spinning
US4381269A (en) * 1980-11-11 1983-04-26 Nippon Telegraph & Telephone Public Corporation Fabrication of a low-loss plastic optical fiber
US4681400A (en) * 1981-08-25 1987-07-21 Sumitomo Electric Industries, Ltd. Plastic optical fibers
US4505543A (en) * 1981-10-14 1985-03-19 Sumitomo Electric Industries, Ltd. Plastic optical fibers
US4511209A (en) * 1982-02-24 1985-04-16 Ensign-Bickford Industries, Inc. Composition having improved optical qualities
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US4544235A (en) * 1982-07-05 1985-10-01 Mitsubishi Rayon Co., Ltd. Plastic optical fibers
EP0107283A2 (en) 1982-08-12 1984-05-02 E.I. Du Pont De Nemours And Company Upholstery support material made of crossed strands of oriented thermoplastic elastomer
US4469738A (en) * 1983-01-21 1984-09-04 E. I. Du Pont De Nemours And Company Oriented net furniture support material
US4469739A (en) * 1983-01-21 1984-09-04 E. I. Du Pont De Nemours And Company Oriented woven furniture support material
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DE2858163C2 (ja) 1989-06-15
JPS5883010A (ja) 1983-05-18
BE871239A (fr) 1979-04-13
JPH0445802B2 (ja) 1992-07-28
GB2006790B (en) 1982-03-31
CA1120197A (en) 1982-03-16
DE2858225C2 (ja) 1988-03-31
NL186527C (nl) 1990-12-17
FR2405806A1 (fr) 1979-05-11
NL7810326A (nl) 1979-04-18
JPS6018963B2 (ja) 1985-05-14
JPS5878103A (ja) 1983-05-11
JPS6018964B2 (ja) 1985-05-14
JPS5465555A (en) 1979-05-26
IT7828756A0 (it) 1978-10-13
GB2006790A (en) 1979-05-10
JPS615206A (ja) 1986-01-11
NL186527B (nl) 1990-07-16
DE2844754A1 (de) 1979-04-26
IT1099911B (it) 1985-09-28
DE2844754C2 (ja) 1987-02-12
FR2405806B1 (ja) 1984-03-23

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